Variable displacement device

ABSTRACT

A positive displacement hydraulic device such as a pump or motor includes a plurality of hydraulically balanced ball piston actuators and pistons which are controllably reciprocated in cylinder bores by a tile plate having a circular groove in which the piston actuator balls roll, the groove having a pair of diametrically opposed depressions disposed opposite to the respective lands in the port plate.

O United States Patent ns1 3,636,82 1 Rystrom [451 Jan. 25, 1972 [54]VARIABLE DISPLACEMENT DEVICE 2,956,895 10/ 1960 Wahlmark ..92/2562,980,077 4/l96l ...92/255 [72] lnventor: Charles H. Rystrom, 696 OakSt., Winnet- 3,274,896 9/1966 ...9l/498 ka, Ill. 60093 3,366,0l7 l/l968...92/178 [22] Filed: Selm lo 1969 3,435,774 4/l969 Parrett ..91/501[2l] Appl. No.: 856,694 Primary Examiner-William L. Freeh Attorney-Fidler, Bradley & Patnaude [52] U.S. Cl ..91/504, 91/475 [51] im. ci.Fo4b1/zo,Foib 13/04 [57] ABSTRACT [58] Field of Search ..92/255-259,[78; A positive displacement hydraulic device such as a pump or 91/499,504 motor includes a plurality of hydraulically balanced ball pistonactuators and pistons which are controllably reciprocated in [56] YReferences Cited cylinder bores by a tile plate having a circular groovein which the piston actuator balls roll, the groove having a pair ofUNITED STATES PATENTS diametrically opposed depressions disposedopposite to the 2,617,360 11/1952 Barker ..91/501 x respective 'ende ithe Pert Plate 2,749,844 6/1956 Weisenbach et al ..91/475 3 Claims, 8Drawing Figures VARIABLE DISPLACEMENT DEVICE The present inventionrelates to positive displacement hydraulic pumps and motors, and itrelates more particularly to such devices employing hydraulicallybalanced ball piston actuators and to hydraulic pumps and motors havingauxiliary depressions in the tilt plate to reduce noise.

Hydraulic pumps of the types using motor driven pistons have, in thepast, had an objectionably high-noise level. The noise comes from twomain sources-high compression and release of the hydraulic fluid in thecylinders as they pass from the inlet to the outlet ports in the valveor port plate, and cylinder block blowot, a condition wherein thecylinder block chatters against the port plate due to unbalanced forcesacting thereon and which is often caused by whipping of the pistonactuator mechanisms.

An object of this invention is to provide a new and improved variabledisplacement hydraulic device which operates at a relatively low-noiselevel.

Another object of this invention is to provide means for minimizingcylinder block blowoff in a hydraulic pump or molOl.

A further object of this invention is to provide a hydraulicallybalanced ball actuator arrangement for use in pumps and motors.

A still further object of this invention is to provide means foreliminating compression of fluid in the cylinders of a hydraulic pump ormotor.

Briefly, the above and further objects may be realized in accordancewith the present invention by providing a pump or motor of the axialpiston type wherein the pistons and piston actuators which arepreferably solid balls, are located within and guided by the cylinderbores in the cylinder block or rotor, and a tilt plate having aplurality of depressions for interrupting axial displacement of thepistons at the'ends of their strokes as they pass from the pressure tothe suction ports of the port or valve plate.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof` will best beunderstood by reference to the following detailed description taken inconnection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a variable displacement hydraulicfluid translating device embodying certain features of the presentinvention;

FIG. 2 is an end view of the device of FIG. 1 taken from the left-handside thereof as viewed in FIG. l and showing the inlet and outlet portsthereof;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1 showingthe arcuate ports in the port plate;

FIG. 4 is a sectional view taken along the line 4-4 in FIG. l showingthe face of the tilt plate;

FIG. 5 is an enlarged view of the device of FIG. l;

FIG. 6 is a greatly enlarged view of a portion of the tilt plate takenalong the line 6-6 in FIG. 4;

FIG. 7 is an alternative embodiment of the piston assembly illustratedin FIG. 5; and

FIG. 8 is still another alternative embodiment of the piston assemblyillustrated in FIG. 5.

Referring now to the drawings, and particularly to FIGS. l and 2thereof, a hydraulic pump or motor 10 includes a mainhousing member orcasing 12 which is secured to a valve or port plate 14 by means of aplurality of bolts 16 to define a chamber 18 into which a main shaft 20extends. The inner end of the shaft 20 is journaled in a bushing 22mounted in a suitable recess in the port plate 14. A ball bearingassembly 24 supports the other end of the shaft 20 within the housing 12and a suitable seal 26 is interposed between the shaft 20 and thehousing 12 to seal off the chamber 18. For the same reason, an O-ring 28is compressed between the housing l2 and the port plate 14. A cylinderblock or rotor 30 is attached to the shaft 20 by means of a spline 32and a tilt plate 34 is carried by means of a pair of conventionaltrunnions (not shown) mounted in the housing 12. As is explained morefully piston assembly in the hereinafter, the tilt plate 34 is pivotablein the plane of the drawing about the centerline 36 and is resilientlybiased into the illustrated position by means of a coil spring 38mounted within the chamber 18 near the top thereof between a shoe 40which fits into a recess 42 in the tilt plate and a button 44 which isattached to the end of a threaded rod 46 which extends through athreaded hole in the housing 12 and over the end of which is mounted acapnut 48 which cooperates with a sealing washer 49 to prevent undesiredleakage from the chamber 18. The chamber 18 may, however, be ported tothe atmosphere by means not shown. The spring pressure on the tilt platecan thus be adjusted by removing the nut 48 and rotating the rod 46. Aplurality of cylinder bores 40 are drilled in the cylinder block 30 andreceive respective ones of an equal number of piston assemblies 52 whichare described more fully hereinafter in connection with FIG. 5. Thebottom (left as viewed in FIG. l) of each of the cylinder bores 50 is incommunication with the face of the port plate I4 by means of a port 54which extends through an annular boss 56 on the rear face of thecylinder block. The adjacent face of the port plate 14 is provided witha pair of arcuate ports 58 and 60 which respectively connect to theinlet and outlets 62 and 64 provided in suitable bosses 65 and 66 in theport plate 14. Between the arcuate ports 58 and 60 are a pair of lands68 and 69 whose arcuate length is greater than the arcuate dimension ofeach of the ports 54 in the cylinder block 30 so that as the ports 54travel between the passageways 58 and 60 and thus travel across the landareas 68 and 69 their associated cylinder bores 50 are completelyisolated from both the inlet and outlet ports 58 and 60 in the portplate 14.

Mounted on and forming a part of the tilt plate 34 is an annular ring orplate 70, which may be made of hardened tool steel and having therein ashallow annular groove 72 in which the piston assemblies ride and whichthus controls the axial reciprocation ofthe piston assemblies in thecylinder bores 50. As best shown in FIGS. 4 and 6, shallow, radiallyextending grooves 74 form very small depressions in the face of the tiltplate into which the pistons fall as their respectively associated ports54 travel across the land areas 68 and 69. Where these land areas arelocated at the top and bottom of the pump, as illustrated in thedrawings, the transverse grooves forming the depressions 74 are likewiselocated at the top and bottom of the plate 70. In other words, thedepressions 74 are located directly opposite to the land areas whichseparate the inlet and outlet ports 58 and 60 at the right-hand face ofthe port plate 14.

Referring now to FIG. 5 for a more complete description of the pistonassemblies 52, each of the piston assemblies includes an imperforateball 76 which fits snugly but movably in a counterbore 78 at theright-hand end of the associated cylinder bore 50. A sleevelike piston79 is fitted into the lower part of the bore 50 and is provided with aplurality of round bottom piston grooves 80. A shoe 81 which is slightlyrockable in the piston 79 is sealed thereto by means of an O-ring 82. Acoil spring 84 is compressed between a button 86 at the bottom of thebore 50 and a shoulder 88 within the sleeve 79 to resiliently urge theentire piston assembly into engagement with the tilt plate assembly.

The shoe 8l which is preferably an investment or precision casting has alongitudinal passageway 89 extending therethrough and a recess 90adjacent to the surface of the ball and defined by an annular seat 92which has a small radius of approximately 0.015 inch on its outer edgeas it leads into the ball equal to that of the ball 76 and which seatson the surface of the ball 76 in a manner permitting rotation of theball as it travels along the groove 72 in the tilt plate during rotationof the cylinder block 30. The seat 92 has a concave portion of about0.047 inch whose radius is equal to that of the ball and adjacent to theconcave portion and forward thereof toward the tilt plate 70 is a smallconvex radius of approximately 0.015 inch to provide a lead in for theball. The effective area of the recess 90 if equal to that of the bore50 whereby there is no hydraulic pressure forcing the shoe 8l againstthe ball. The

only frictional force exerted between the seat 92 and the ball 76 isthat caused by the spring 84 which may have a relatively low springconstant and yet maintain the ball 76 in engagement with the tilt plate70. Hence, the ball 76 rotates rather freely as it rolls along thegroove 72 thus increasing the efficiency of operation of the device. Arelief hole 93 is drilled into the counterbore 78 to prevent entrapmentof hydraulic fluid behind the ball 76.

In the embodiment ofthe piston assembly illustrated in FIG. 7, thegenerally cylindrical sleeves 79 of FIG` l has been replaced with ahemispherical piston 79 which may be half of a ball bearing throughwhich longitudinal bore and counterbore have been provided by means ofan E.C.M. machine. A centrally apertured, conical button 94 fits intothe left-hand end of the hemisphere 79 and a coil spring 9S urges theentire piston Q, ssembly into engagement with the tilt plate 70. Sincethe piston 79' cannot bottom in the cylinder bore 50, the need for arelief counterbore at the bottom is eliminated.

In the embodiment of FIG. 8 the piston comprises a pair of back-to-backmounted hemispheres 96 and 97 which replace the single hemisphere 79' ofFIG. 7 and the button 94 of FIG. 7 is replaced with a somewhat longerbutton 98, the shank of which extends completely through the hemisphere94 into the hemisphere 97.

OPERATION While the hydraulic fluid translation device l of the presentinvention finds application as either a pump or a motor, its operationwill be described hereinafter as a pump, it being understood that thoseskilled in the art will thereby readily understand its operation as amotor.

With the inlet and outlet ports 62 and 64 connected in a suitablepumping loop or circuit, and the shaft connected to a suitable drivesource whereby it is driven in a counterclockwise direction as viewedfrom the right-hand side of FIG. 1, as the particular piston assembly 52which is disposed at the bottom moves upwardly, the ball 76 thereofrolls along the groove 72 in the tilt plate and under the force ofthespring 84 it moves outwardly of the cylinder bore S0 thereby drawinghydraulic fluid from the inlet 62 through the passageway 58 in the portplate 14 and through the port S4 to fill the void created by the pistonS2 moving outwardly of the cylinder bore. When this particular pistonassembly has reached the top of the chamber I8, it is at the fullyextended position and at this time it rides down along asinusoidal-shaped surface portion 99 of the depression or groove 74 andonto the flat or planar bottom of the groove 74. With balls 76 having adiameter of seven-eighths of an inch this entire groove 74 may have across-sectional width of five thirty-seconds of an inch, the flatportions being 0.052-inch wide. At this same time, the port 54 ispassing across the land area 68 and since the piston is now axiallystationary within the bore S0 there is no force exerted on the fluidwithin the cylinder bore S0. As the piston assembly now crosses the landarea 68 and the port 54 moves into communication with the outlet 60, thepiston assembly moves axially into the bore 50 thereby forcing the fluidpreviously drawn therein into the outlet port 60 and thus out of theoutlet 64, When the piston assembly 52 again reaches the bottom of thechamber I8 it will have completed one cycle of reciprocation as ittravels into the lower depression or groove 74 just before the port 54passes onto the land area 69.

lt will be understood that the number of bores 50 and associated pistonassemblies 52 which are used may vary from one application to anotherbut for most purposes nine such bores and associated assemblies will beused. Where, however. the device is to be used as a reversing pump, aneven number, such as eight pistons should be used, the spring 38replaced with hydraulic cylinders, and the pivot axis of the trunnionsmoved from the location indicated at 36 in FIG. l to the longitudinalaxis of the shaft 20. Also, it will be understood that the spring 38 andthe associated parts, which are conventional in these types of devices,may be re laced with hydraulic or other means for varying the angle othe tilt plate, thereby to vary and automatically adjust the strokes ofthe piston assemblies to compensate for the changing load conditions.

lnasmuch as the piston assemblies 50, including the ball pistonactuators 76 are located within the bores 50 and the balls 76 providethe only variable mechanical force on the pistons, there is no angularthrust exerted on the cylinder block whereby it is at all timesangularly balanced to minimize deflection of the shaft 20 and axialmovement of the cylinder block relative to the port plate.

What is claimed is:

1. A variable pressure hydraulic fluid energy translating device of thetype including a port plate having a plurality of spaced arcuate portstherein separated by land areas,

a cylinder block rotatable with respect to said port plate and having aplurality of bores opening into said port plate for sequentialcommunication with said ports during rotation of said cylinder block,and

an angularly adjustable tilt plate for controlling the stroke of aplurality of piston assemblies reciprocably mounted in said bores,

said piston assemblies each including a freely rotatable ball disposedin and rolling around a circular groove in the face of said tilt plateas said cylinder block rotates, characterized by a plurality of radialgrooves in said tilt plate extending below the bottom of said circulargroove and respectively positioned along said circular groove oppositesaid land areas for permitting said piston assemblies to move into saidradial grooves when said bores are disconnected from said ports.

2. A device according to claim 1 wherein said cylinder block is providedwith a plurality of connec'tor ports connecting said bores to said portplate,

said connector ports having an arcuate length less than the arcuatelength of said land areas, and

said radial grooves each have a width less than the arcuate length ofsaid connector ports.

3. A device according to claim l wherein said bores are counterbored,

said balls are disposed in the counterbores, and

said piston assemblies each comprise a generally cylindrical sleeve anda pair of hemispheres.

1. A variable pressure hydraulic fluid energy translating device of thetype including a port plate having a plurality of spaced arcuate portstherein separated by land areas, a cylinder block rotatable with respectto said port plate and having a plurality of bores opening into saidport plate for sequential communication with said ports during rotationof said cylinder block, and an angularly adjustable tilt plate forcontrolling the stroke of a plurality of piston assemblies reciprocablymounted in said bores, said piston assemblies each including a freelyrotatable ball disposed in and rolling around a circular groove in theface of said tilt plate as said cylinder block rotates, characterized bya plurality of radial grooves in said tilt plate extending below thebottom of said circular groove and respectively positioned along saidcircular groove opposite said land areas for permitting said pistonassemblies to move into said radial grooves when said bores aredisconnected from said ports.
 2. A device according to claim 1 whereinsaid cylinder block is provided with a plurality of connector portsconnecting said bores to said port plate, said connector ports having anarcuate length less than the arcuate length of said land areas, and saidradial grooves each have a width less than the arcuate length of saidconnector ports.
 3. A device according to claim 1 wherein said bores arecounterbored, said balls are disposed in the counterbores, and saidpiston assemblies each comprise a generally cylindrical sleeve and apair of hemispheres.